CPIDE
CPIDE is a free online IDE with a built-in judge for competitive programming.
You write code in the browser, add test cases, press Ctrl+R, and the server compiles
and runs everything, then compares output against your expected answers — Accepted, Wrong Answer
with a first-difference view, Time Limit Exceeded, Runtime Error or Compilation Error, the same
verdicts a real online judge gives.
No signup. Nothing to install.
Why it exists
Practicing for contests usually means juggling an editor, a terminal, input files and manual diffing — or pasting code into an online compiler that runs one input at a time with no verdicts. CPIDE folds that whole loop into one page: problems, test cases, compiler and judge together.
What it does
- Six languages — C++ (GCC,
-std=c++23), C, Python, Java, Kotlin and Ruby, always current versions. - Contest import — paste an AtCoder or CodeChef URL, or use the one-click bookmarklet on any Codeforces problem or contest page. Every problem arrives as a tab with its sample tests and real time limit.
- Real judging — multiple test cases per problem, compile-once-run-all, hard kills at the time limit, Codeforces-style output comparison.
- A serious editor — Monaco (the editor inside VS Code) with autocomplete,
#includesuggestions and algorithm snippets likedsu,sieve,fenwickanddijkstra. - Everything autosaves — code per problem per language, test cases and settings, stored in your browser.
FAQ
Is it free?
Yes — no account, no ads.
Where is my code stored?
In your own browser. It is sent to the server
only to compile and run, kept only in a temporary build cache, and there is no database.
Why does it sometimes say "server busy"?
Submissions judge one at a time
on free hosting so timing stays accurate. Wait a few seconds and run again.